This invention relates to oil and gas drilling, and more particularly to apparatus and methods for reliably transmitting information between downhole drilling components.
For the past several decades, engineers have worked to develop apparatus and methods to effectively transmit information from components located downhole on oil and gas drilling strings to the ground's surface. Part of the difficulty of this problem lies in the development of reliable apparatus and methods for transmitting information from one drill string component to another, such as between sections of drill pipe. The goal is to provide reliable information transmission between downhole components stretching thousands of feet beneath the earth's surface, while withstanding hostile wear and tear of subterranean conditions.
In an effort to provide solutions to this problem, engineers have developed a technology known as mud pulse telemetry. Rather than using electrical connections, mud pulse telemetry transmits information in the form of pressure pulses through fluids circulating through a well bore. However, data rates of mud pulse telemetry are very slow compared to data bandwidths needed to provide real-time data from downhole components.
For example, mud pulse telemetry systems often operate at data rates less than 10 bits per second. At this rate, data resolution is so poor that a driller is unable to make crucial decisions in real time. Since drilling equipment is often rented and very expensive, even slight mistakes incur substantial expense. Part of the expense can be attributed to time-consuming operations that are required to retrieve downhole data or to verify low-resolution data transmitted to the surface by mud pulse telemetry. Often, drilling or other procedures are halted while crucial data is gathered.
In an effort to overcome limitations imposed by mud pulse telemetry systems, reliable connections are needed to transmit information between components in a drill string. For example, since direct electrical connections between drill string components may be impractical and unreliable, converting electrical signals to magnetic fields for later conversion back to electrical signals offers one solution for transmitting information between drill string components.
Nevertheless, various factors or problems may make data transmission unreliable. For example, dirt, rocks, mud, fluids, or other substances present when drilling may interfere with signals transmitted between components in a drill string. In other instances, gaps present between mating surfaces of drill string components may adversely affect the transmission of data therebetween.
Moreover, the harsh working environment of drill string components may cause damage to data transmission elements. Furthermore, since many drill string components are located beneath the surface of the ground, replacing or servicing data transmission components may be costly, impractical, or impossible. Thus, robust and environmentally-hardened data transmission components are needed to transmit information between drill string components.